Optimization of PCB Dechlorination with Palladized Magnesium in Marine and Freshwater Sediments

Irina Calante, an Environmental Engineering graduate student at UNH, is working with Dr. Kevin Gardner on in-situ remediation of contaminated marine and freshwater sediments. Irina's specific aspect of the research is to optimize the dechlorination of polychlorinated biphenyls (PCBs) in sediment with different reducers by determining rate limiting factors through sediment characterization, reducer concentration, and rate of reaction. The reducer of focus is zero valent palladized magnesium (Mg/Pd) where the magnesium is the reactant and the palladium acts as a catalyst only. The main objective is to create a remediation technology for PCB contaminated sediments that actually degrades the PCBs. This technology would be able to be applied in-situ as well as ex-situ. It would provide an alternative to the most common remediation methods used today, dredging and caping, which isolate the contaminant but do not reduce its concentration.

Bench scale experiments so far have shown dechlorination of PCBs in sediments with Mg/Pd (Figure 1). The dechlorination efficiency is dependent on the initial PCB concentration in the sediment, the organic content, the sediment composition as well as the amount of Mg/Pd. Desorption experiments have also been conducted to determine whether PCB desorption from the sediment is a limiting factor for dechlorination (Figure 2). Based on the dechlorination efficiency achieved so far, desorption does not seem to be a rate limiting step. However, it might be rate limiting for the most inaccessible PCBs confined in the sediment. Solvent experiments were conducted to see if solvents would increase the availability of the PCBs from the sediment. The addition of two terpene based solvents did not improve overall dechlorination wit Mg/Pd when compared to the addition of water (Figure 3).

Figure 1. Cumulative percent PCB desorption from two sediments, Housatonic River and New Bedford Harbor, over 50 days.